A device which simultaneously measures a leakage current flowing through a predetermined electric circuit as a zero phase current I0 and extracts and measures a leakage current I0r which is a component caused by a ground insulation resistance value in the electric circuit, from the zero phase current I0 has been known.
For example, a leakage current measurement device (hereinafter, referred to as a “device 1”) disclosed in Patent Document 1 measures a R phase and T phase interline voltage VRT (alternatively, a T phase and S phase interline voltage VTS or an S phase and R phase interline voltage VSR) on a secondary side of a three phase transformer in which secondary windings are connected in a delta (Δ) type, measures a zero phase current I0 flowing through a distribution line which connects the secondary side of the three phase transformer and a load device, calculates a phase difference of a reference voltage and the zero phase current I0 when the interline voltage VRT (alternatively, VTS or VSR) is considered as the reference voltage, and calculates an effective component as the leakage current I0r by dividing the zero phase current I0 into an effective component which has the same phase as the reference voltage and an ineffective component which has a phase difference of 90 degrees with respect to the reference voltage.
The device 1 is configured such that even when the load device (for example, a motor) is in a driving state and an electric circuit is in a hot-line state, the leakage current I0r is calculated.